add updated composer autoloader code

lib/composer/composer/ClassLoader.php

@@ -53,8 +53,8 @@ class ClassLoader
 
     private $useIncludePath = false;
     private $classMap = array();
-
     private $classMapAuthoritative = false;
+    private $missingClasses = array();
 
     public function getPrefixes()
     {
@@ -322,20 +322,20 @@ class ClassLoader
         if (isset($this->classMap[$class])) {
             return $this->classMap[$class];
         }
-        if ($this->classMapAuthoritative) {
+        if ($this->classMapAuthoritative || isset($this->missingClasses[$class])) {
             return false;
         }
 
         $file = $this->findFileWithExtension($class, '.php');
 
         // Search for Hack files if we are running on HHVM
-        if ($file === null && defined('HHVM_VERSION')) {
+        if (false === $file && defined('HHVM_VERSION')) {
             $file = $this->findFileWithExtension($class, '.hh');
         }
 
-        if ($file === null) {
+        if (false === $file) {
             // Remember that this class does not exist.
-            return $this->classMap[$class] = false;
+            $this->missingClasses[$class] = true;
         }
 
         return $file;
@@ -399,6 +399,8 @@ class ClassLoader
         if ($this->useIncludePath && $file = stream_resolve_include_path($logicalPathPsr0)) {
             return $file;
         }
+
+        return false;
     }
 }